Field of the Invention
The present invention relates to a Liquid Crystal Display (LCD) device, and more particularly, to an LCD device having a built-in touch panel and a method of driving the same.
Discussion of the Related Art
LCD devices adjust the light transmittance of liquid crystal with an electric field to display an image. To this end, the LCD devices include a liquid crystal panel in which a plurality of pixels are arranged in a matrix type, and a driver for driving the liquid crystal panel.
Methods, which input a control signal into an electronic product with LCD devices mounted thereon, include a method using a touch panel and a method using buttons. Recently, the method using the touch panel is widely used.
LCD devices with a touch panel mounted thereon are being applied to various electronic products such as navigations, industrial terminals, tablet PCs, smart phones, financial automation equipments, game machines, etc. Also, the LCD devices are being expanded in application because all users can easily manipulate the LCD devices with touch screen.
FIG. 1 is an exemplary diagram for describing a related art method of driving a touch panel. FIG. 2 is an exemplary diagram illustrating various types of LCD devices with a touch panel. A touch panel shown in a portion (a) of FIG. 2 is an on-cell type, a touch panel shown in a portion (b) of FIG. 2 is a hybrid in-cell type, and a touch panel shown in a portion (c) of FIG. 2 is an in-cell type. In FIG. 2, reference numeral 31 is a TFT substrate, reference numeral 32 is a color filter substrate, reference numeral 33 is a liquid crystal layer, and reference numeral 34 is glass.
A touch panel 40 detects a touch generated by a user. Touch panels may be categorized into a resistive type, a capacitive type, etc. Hereinafter, however, a capacitive type touch panel will be described.
A touch panel 40 includes a driving electrode 11 to which a driving voltage is applied and a receiving electrode 21 receiving a sensing signal generated by a driving voltage. A touch sensing unit 60 includes a driving voltage generator 61 applying a driving voltage to the driving electrode 11 and a sensing signal receiver 62 determining whether there is a touch by using a sensing signal received through the receiving electrode 21.
A touch panel 40 may be formed in various types depending on a disposed position.
First, as shown in a portion (a) of FIG. 2, the touch panel 40 may be adhered to an upper end surface of a color filter substrate 32, namely, the touch panel may be configured in an on-cell type.
Second, as shown in a portion (b) of FIG. 2, one of two electrodes 11 and 21 configuring the touch panel 40 may be formed in the TFT substrate 31 of the LCD device, and the other may be formed in an upper end surface of a color filter substrate 32, namely, the touch panel 40 may be configured in a hybrid in-cell type.
Third, as shown in a portion (c) of FIG. 2, two electrodes 11 and 21 configuring a touch panel 40 may be formed on the same layer of a TFT substrate 31 configuring a LCD device, namely, the touch panel 40 may be configured in an in-cell type. The two electrodes 11 and 21 applied to the in-cell type touch panel are respectively used as a driving electrode and a receiving electrode for a touch sensing period. However, all of the two electrodes are used as common electrodes receiving a common voltage for an image display period.
FIG. 3 is various waveform diagrams illustrating an image display period and a touch sensing period in a related art LCD device.
A portion (a) of FIG. 3 shows an image display period in a normal LCD device with no touch panel. A waveform shown in the portion (a) of FIG. 3 may be a vertical sync signal Vsync. In this case, one frame period includes an image display period (display) for which an image is displayed and a blank period for which an image is not displayed.
A portion (b) of FIG. 3 shows an image display period and a touch sensing period in the LCD device (hereinafter referred to as “in-cell type LCD device”) with the in-cell type touch panel built therein.
The related art in-cell type LCD device has the following limitations.
First, as shown in the portion (b) of FIG. 3, in the in-cell type LCD device, the two electrodes configuring the touch panel are used as the common electrode, and thus, an image display operation and a touch sensing operation cannot simultaneously be performed. Therefore, as shown in the portion (b) of FIG. 3, one frame period includes an image display period (display) and a touch sensing period (touch).
When a LCD device is driven at a frequency of 60 Hz, one frame period is set to a time of 16.7 ms. Therefore, as resolution and a size of a liquid crystal panel increase, a driving period for one channel becomes relatively shorter. In this case, an image display function and a touch sensing function can be degraded in performance due to an insufficient charging time.
That is, as shown in the portion (b) of FIG. 3, in the in-cell type LCD device, it is required to divide the image display period and the touch sensing period. Therefore, as a size of the liquid crystal panel increases, the number of channels increases, and thus, the image display function and the touch sensing function can be degraded in performance.
Second, in the in-cell type LCD device shown in the portion (b) of FIG. 3, because a direction of a data line does not match a direction of the receiving electrode 21, the in-cell type LCD device is vulnerable to a data noise. That is, because a sensing signal induced by the driving voltage supplied to the driving electrode 11 is transferred to the sensing signal receiver 62 through the receiving electrode, more noise is generated in the receiving electrode 21 than the driving electrode 11. Therefore, there is much possibility that a noise is generated in a data line disposed in parallel to the receiving electrode.